This invention relates to the removal and the recovery of metal compounds from brines. In particular, it relates to the removal and the recovery of compounds containing magnesium, strontium and barium from brines.
Brines, such as Smackover formation well brines, contain a variety of metals including magnesium, strontium and barium. A number of processes have been proposed for the removal and the recovery of these metals.
The removal and the recovery of magnesium, strontium and barium from brines provides two important commercial advantages. First, the recovered compounds of these metals can be sold on an open market. Second, the removal of these metals from brines permits the recovery of valuable lithium from brines in an uncontaminated, more valuable form. See, e.g., U.S. Pat. No. 4,271,131 (Brown, et al.) and U.S. Pat. No. 4,261,960 (Boryta) column 1, lines 40-49.
Magnesium can be removed and recovered from brines by contacting it with lime to form a precipitate of magnesium hydroxide. Generally, such precipitates are slow settling and difficult to separate from the mother liquor by filtering. See, e.g., U.S. Pat. No. 2,405,055 (Robinson, et al.), column 1, lines 7-16; Kirk-Othmer, 12 Encyclopedia of Chemical Technology (2 ed.) p. 729. Since quicker settling and filterable precipitate would reduce capital and operating costs, efforts have been made to improve the basic process for recovering magnesium. For example, the Robinson patent discloses that a magnesium hydroxide precipitate which settles more rapidly can be produced "by diluting the sea water with water or brine free from dissolved magnesium salts, before or at the time of precipitation, accompanied by a suitable control of the amount of alkali", column 3, lines 39-42. Similarly, U.S. Pat. No. 2,191,560 (Farnsworth, et al.) discloses that settling characterstics of a magnesium hydroxide precipitate can be enhanced by reacting lime with brine at temperatures above 105.degree. F. and preferably at about 140.degree. F. See column 2, lines 6-9.
U.S. Pat. No. 3,080,215 (Waldron, et al.) discloses a method for improving the poor filterability of a precipitate of magnesium hydroxide when separating it from the mother liquor. The method includes the use of slaked calcined dolomite slurry and reaction conditions that include temperatures of 40.degree. to 80.degree. C. See column 2, lines 27-41. The Waldron patent discloses that the precipitate form using its process is readily filterable. See column 2, lines 42-43.
It is also known that strontium can be removed from brines by contacting them with sodium sulfate. The contacting produces a precipitate which contains primarily strontium sulfate but includes about 2 weight percent of barium sulfate. Strontium-barium sulfate is useful but its price is relatively low because it is in competition with celestite, a mineral found in many countries including Mexico. Since barium is difficult and expensive to separate from strontium, the usefulness of the removed precipitate as the source of pure strontium is diminished by the presence of the barium contaminant. Additionally, the conversion of strontium-barium sulfate to a desired strontrium compound--strontium carbonate--is costly and laborious.
There is therefore a need for a process which would inexpensively and efficiently remove magnesium, strontium, and barium from brines and recover these metals in the form of uncontaminated desired compounds.
Thus, one object of the present invention is to provide an efficient process for sequentially removing and recovering from brines magnesium, strontium which is uncontaminated by barium, and barium.
Another object of the present invention is to provide an energy-efficient process for sequentially removing and recovering uncontaminated strontium and barium from brines.
Still another object of the present invention is to provide a process for recovery of strontium from brines in the form of a compound which can be easily converted into a commercially desirable strontium carbonate.
A further object of the present invention is to provide a process for the removal and the recovery of magnesium, strontium and barium, which process utilizes the natural heat of brines.
Still another object of the present invention is to provide a process for removing and recovering magnesium, strontium and barium, which process produces a fast-settling, easily filterable precipitate containing magnesium.
A still further object of the present invention is to provide a process which quickly and efficiently removes magnesium, strontium and barium from brines so that high purity lithium can be recovered from the remaining mother liquor.
Other objects of the present invention will become apparent to those skilled in the art upon studying this disclosure.